The metabolism of cholesterol and fatty acids, essential components of many biochemical pathways, is tightly regulated at the cellular level. Insufficient or excess levels can be detrimental to cells and are associated with aging-related diseases such as atherosclerosis, type 2 diabetes, and metabolic syndrome. Many regulatory pathways exist to ensure that cholesterol and fatty acid levels are balanced. In particular, recent findings have revealed a crucial role for small non-coding RNAs (miRNAs) in the post-transcriptional control of cholesterol and lipoprotein-related genes. Of note is microRNA-33 (miR-33), an intronic miRNA located within the sterol regulatory element-binding protein (SREBP) gene, one of the master regulators of cholesterol and fatty acid metabolism. miR-33 regulates cholesterol efflux and high density lipoprotein (HDL) formation in concert with the SREBP host genes, suggesting an important role for miRNAs in the regulation of cholesterol metabolism. miR-33 has also recently been to shown to regulate fatty acid metabolism and insulin signaling. miR-33 binds and represses key enzymes involved in the regulation of fatty acid oxidation, including carnitine O-octaniltransferase (CROT), carnitine palmitoyltransferase 1A (CPT1a), and hydroxyacyl-CoA-dehydrogenase (HADHB). In addition, miR-33 also targets the insulin receptor substrate 2 (IRS2), an essential component of the insulin- signaling pathway. Overexpression of miR-33 reduces both fatty acid oxidation and insulin signaling in hepatic cell lines, whereas endogenous inhibition of miR-33 increases these two metabolic pathways. In this proposal, we hypothesize that miR-33 regulates pathways controlling three of the risk factors of metabolic syndrome, including levels of HDL, triglycerides, and insulin signaling and that miR-33 may be useful as a therapeutic target to treat this growing health concern. PUBLIC HEALTH RELEVANCE: The research proposed has significant implications in the field of lipid biology and cardiology- both key issues in aging that impact mortality and quality of life This work is intended to characterize a novel regulator of cholesterol, lipid, and glucose metabolism in liver cells and in mice fed a chow and high-fat diet. This work will also address how this regulator may impact risk factors that increase the chance of developing heart disease, stroke, and type 2 diabetes- important diseases and consequences of aging.